Thermo-ecological evaluation of an integrated MILD oxy-fuel combustion power plant with CO₂ capture, utilisation, and storage – A case study in Poland

This study investigated the environmental benefits of a new boiler design for a fossil fuel-based power plant with CO₂ capture, utilisation, and storage (CCUS) through thermo-ecological cost (TEC) analysis. MILD oxy-fuel combustion (MOFC) combines the advantages of the moderate and intense low-oxygen dilution (MILD) combustion and oxy-fuel combustion (OFC) to achieve efficient and environmentally justified CO₂ capture from fossil fuel-based power generation. The advantages of MOFC application are: (i) it increases the efficiency of the coal-fired boiler, (ii) it increases the purity of the CO₂ in the flue gases, (iii) it reduces the oxygen consumption of the boiler by using lower oxidiser excess, and (iv) it reduces the energy consumption associated with CO₂ recirculation. Therefore, using MOFC decreases the penalty of the overall net energy efficiency associated with the CO₂ capture from coal-fired power plants. The environmental analysis in this study considered the TEC, which measures the depletion of non-renewable natural resources by estimating the cumulative exergy consumed by the production processes. Moreover, the additional exergy consumption that compensates for the negative impact of harmful emissions has also been considered. The data for the new boiler design were obtained by CFD modelling, while the other technological modules of the integrated MOFC power plant were modelled by process modelling software. The data concerning the CO₂ transport, utilisation, and storage were obtained from the available databases and literature. Three configurations of the power plant were modelled and analysed from the environmental point of view. The first two were the reference coal-fired power plants (the conventional power plant and the oxy-fuel combustion power plant with CO₂ capture), while the third case used the same power plant configuration but with an MOFC boiler. The results were compared to other CO₂ capture options, such as post-combustion, using the electro-energy system in Poland as the reference. The results emphasised the importance of the emissions and energy consumption occurring upstream (e.g. coal extraction and transport) and downstream (e.g. CO₂ transport and storage) of the project when assessing the environmental impact factors. Additionally, two industrial options for CO₂ utilisation were proposed, because CO₂ storage is generally opposed by the public.